4. Influence of the
heating on the attractive force of a magnetic attachment
-Part 2. Study of
Denture Based Resin Curing-
Miyata
T., Nakamura Y., Niimi J., Ando A., Shouji k., Imaoka S., Ohno Y., and Tanaka
Y.
Removable
Prosthodontics,
Introduction
A magnetic
attachment has achieved excellent clinical results, and has been recognized as
a useful tool with numerous advantages compared with a conventional mechanical
retainers1-3).
A Neodymium
(Nd) magnet, recently available on the market, has a reported characteristic
the temperature-related of magnetic force loss at low relative
temperatures. This is considered as
one disadvantage of a Nd magnet use.
The clinical
use conditions including the effect of temperature relationship and laboratory
processing should be evaluated.
Objective
We
investigated the influence of the difference in curing methods and thickness of
denture-base resin on the attractive force of a magnetic attachment on the
assumption that magnetic assemblies were incorporated into the work model
during polymerization temperatures.
Materials and Methods
1)
Materials
Specified magnetic
assemblies and keepers were used as samples in this study (GIGAUSS D 600 (GC)
and PHYSIO MAGNET 35 (Hitachi Metals)).
Five samples for each product were evaluated(Fig. 1).
Fig. 1: Magnetic attachments
2)
Methods
The influence of two
different resin curing protocols were tested on magnetic attachment attractive
force: 1. microwave curing method and 2.wet heat curing method.
Resin curing protocol
with magnetic attachments followed the following techniques. Microwave technique resins were cured in
a specified microwave oven at 500 watts for 3 minutes. Wet heat resin curing protocol were
cured at 70°C for 60 minutes, and then 100°C for 30 minutes, followed by
cooling at room temperature for 24 hours.
Following use of either curing method, tested magnetic assemblies were
removed from resin samples, and attractive force was measured. Attractive forces before and after
polymerization for each curing method were compared to investigate the
influence of polymerization on the attractive force. We also investigated the change in the
attractive force for 3 different resin thicknesses.
3)
Sample preparation
Molded paraffin wax was
invested in a flask using ADVASTONE (GC) based on the conventional method,
followed by wax elimination. A
magnetic assembly was adhesively stablized with alpha-cyanoacrylate adhesive
(Aron Alpha) into the space created by wax elimination. Acron MC Live Pink no. 8 was packed into
a flask in the rapid heat cure method, and Acron Live Pink no. 8 was packed in
the wet heat cure method. A
magnetic assembly was removed from the resin plate after polymerization, and
used as a sample (Fig. 2). Resin
plate samples were 35 x 60 mm in width, and 5, 10, and 15 mm in thickness (Fig.
3).
Fig. 2: Process of sample fabrication Fig. 3: Resin plate size size
4)
Attractive force measurement
Attractive force
measurement was conducted using EZ test, compact tabletop material tester, with
a 5 kgf load cell and 5 mm/min crosshead speed. Attractive force was measured 10 times
for each magnetic assembly, and the average was taken as a result. Attractive forces before and after each
experiment were compared. The custom made jig devised in our department was used
to accurately measure the attractive force (Fig. 4).
Fig. 4: Measuring device and custom made jig
Results
In the rapid
heat cure method, magnetic attraction forces decreased with both in GIGAUSS D
600 and PHYSIO MAGNET 35 after completion of polymerization procedures. The evaluation of resin thickness on the
attraction forces demonstrated a decrease in measured attraction force with the
resin plate thickness of 10 mm compared to a 5mm sample. No significant difference was found for
the 10 and 15 mm samples (Fig. 5).
The wet heat
curing method showed similar results as the rapid heat curing method regarding
the influence of curing methods and resin thickness (Fig. 6).
Discussion
The present
study was performed on the basis that magnetic assemblies are incorporated into
working models during higher polymerization temperatures. Magnetic assemblies were directly bonded
with a heat-curing resin. Since
this method does not require autopolymerized quick cure resin, it offers
advantages such as improved mucosal surface denture esthetics, and improved
adhesive attachment between a magnetic assembly and resin. Dentures made using
this procedure offer several advantages and improved physical properties with
greater material stability.
The influence
of polymerization on the resulting magnetic attachment attractive force
properties is significant.
Attraction forces decreased both with the rapid heat curing method and
wet heat curing method after polymerization. This finding suggests a
significant heat-related material changes after polymerization.
The magnetic
attachment attraction forces are also affected by enclosing denture resin base
thickness. Further investigation in the relationships of heating on the
magnetic assembly units is recommended.
The mechanisms of heat generation and polymerization on the attractive
force are not clearly understood.
It is also unclear as to the influence of electromagnetic microwave
generation on magnetic assemblies and metal components.
Conclusion
The influence of two different denture
resin curing protocols of the denture base resin, and the effect of resin
thickness on the attraction force was evaluated.
1.Both
the microwave and wet heat curing methods showed a decrease in the attraction
force after polymerization.
2.The
attractive force decreased by 4% in a resin plate 5 mm in thickness, and by 10%
in a resin plate 10 mm in thickness.
No difference was found between resins 10 and 15 mm in thickness.
3.No
significant difference in the attractive force of a magnetic assembly was found
between rapid and wet heat resin curing techniques.
Reference
1.
2. Tanaka, Y.: Dental Magnetic
Attachment, Q＆A, Ishiyaku Publishers, Inc.(
3. Nakamura, K. Hiroshi, M. Fukazawa, N.
and et al: Influence of Heat Treatments on Attractive Force of Magnetic
Attachments. J J Mag Dent. 6: 63-70, 1997.